Fortunately, it is possible to convert back from an LDM to a standard setup, but you'll need to use third-party utilities. EaseUS Partition Master and Partition Wizard are both supposed to be able to do this, IIRC. (Double-check this, though; my memory may be faulty, and I've never used either tool myself.) I recommend doing a complete backup before using either tool, since partitioning operations like this are inherently risky.

So far I've been unable to to verify that my setup indeed is what is described in this answer. What keeps bugging me is that Ubuntu can read from and write to my Windows 7 partition just fine when run from a live USB stick. Gparted just sees the disk in this wicked awesome way described in my original question.
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KalljaApr 29 '13 at 14:18

You can verify this in several ways. One is in Linux: Type sudo fdisk -l /dev/sda to see the partitions on your disk with their type codes, which are under the Id column in the fdisk output. If the type codes for your partitions are 42, then you've got an LDM setup. (The number of partitions shown may not match the number in Windows, too.) Another way is in Windows: Use the Windows partitioning tool to view your partitions. If it shows them as being "dynamic" disks, then you've got an LDM setup; but if it says you've got "basic" disks, then you've got a conventional MBR setup.
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Rod SmithApr 29 '13 at 15:58

First thing I did was check the setup with Windows' disk management. It indicated that all of the partitions were of the basic type. I've since given up on this method of installation. Since my Windows setup was a fairly fresh one, I opted to first install Ubuntu followed by a Windows installation formatting the whole disk in the process.
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KalljaMay 3 '13 at 7:07